A show that is similar to "Buffy" in several ways, especially in its second and final season, is "Dark Angel," starring a young, pre-blond Jessica Alba. Some of people here dismiss the show as just a Buffy rip-off, but it's still fun to watch, if for no other reason than to hunt all of the parallels between the two shows. There are also 3 novels based on the show, all written by Max Allan Collins, who does at least as good a job with his subject as any of the more popular Buffy/Angel writers did, and seems to me at least to write on a bit more mature level than the "young adults" level of the Buffy books.
"Alias" is good, too, for its action scenes if nothing else, and you could make a game out of counting the number of hallways that the actors run down in each season.
"Highlander: The Series" is good for its action and fantasy content. Adrian Paul is a skilled martial artist and swordsman, and the fight scenes are some of the finest that have ever been seen on tv.
"Tru Calling" only lasted a season and a half, but what there was of it is worth watching, if only to see Eliza Dushku in her own series.
"Moonlight" was pretty good, but it only lasted the one season, and as far as I know isn't available on disc yet.
Another vampire show that IS available on disc is "Forever Knight" about a vampire police officer. I never got to watch much of it, but what I saw was pretty good.
About the closest to the vampire slayer genre, though, is currently into it's third(?) season, "Supernatural," about two brothers who are demon hunters. It's a sort of "Buffy meets Route 66" if you're familiar with that old show.